In 1976, Yakimovsky and Cunningham wrote an article entitled “A System for Extracting Three-Dimensional Measurement from a Stereo Pair of TV Cameras”. The article, which was published in Computer Graphics and Image Processing 7, 195-210 (1978), is incorporated in its entirety by this reference. Through a complex series of modeling, calculation, and calibration, the article discloses the calculation of an exact position of each camera, which facilitates the direct triangulation of a three dimensional position of an object.
U.S. Pat. No. 6,101,455, which is incorporated in its entirety by this reference, was issued on 8 Aug. 2000 to Michael S. Davis, one of the teachers of one of the inventors of the present invention. The '455 patent, which references the Yakimovsky and Cunningham article, discloses an automatic calibration of the cameras within a system. The '455 patent discloses a technique that includes calibrating the cameras to a common coordinate frame and moving an object a known relative distance, to determine the positions of the cameras using a vector relationship. The '455 patent does not, however, discloses the use of more than two cameras.
U.S. Pat. No. 6,064,756, which is incorporated in its entirety by this reference, was issued on 16 May 2000 and is currently assigned to Scanner Technologies Corporation. The '756 patent discloses a three dimensional inspection apparatus for ball array devices and, in one embodiment, discloses the use of three cameras. The '756 patent discloses, however, the use of triangulation to calculate a three dimensional position of the ball of a ball array device with reference to a pre-calculated calibration plane, and discloses neither the calculation of the exact position of each camera nor the direct triangulation of the three dimensional position of the ball of a ball array device.
The conventional techniques in the art, while suitable for certain applications, are not suitable for the accurate metrology of the body and connecting terminals (leads, ball grids, bumps, pads) of rapidly moving semiconductor or packaged electronic components in various manufacturing stages. The conventional techniques are simply not suitable for the inspection in such confined environments of deformation of the connection terminals in the semiconductor or packaged electronic components. In these environments, the errors introduced by the conventional techniques in the art, including both statistical error (caused by random, and therefore inherently unpredictable, fluctuations in the measurement apparatus) and systematic error (caused by an unknown but nonrandom fluctuation).
Thus, there is a need in the machine vision field to create an improved machine vision system that reduces the statistical and systematic errors to become suitable for the three-dimensional metrology and inspection in the semiconductor industry. This invention provides such improved machine vision system.